1wpa_supplicant and Wi-Fi Protected Setup (WPS) 2============================================== 3 4This document describes how the WPS implementation in wpa_supplicant 5can be configured and how an external component on the client (e.g., 6management GUI) is used to enable WPS enrollment and registrar 7registration. 8 9 10Introduction to WPS 11------------------- 12 13Wi-Fi Protected Setup (WPS) is a mechanism for easy configuration of a 14wireless network. It allows automated generation of random keys (WPA 15passphrase/PSK) and configuration of an access point and client 16devices. WPS includes number of methods for setting up connections 17with PIN method and push-button configuration (PBC) being the most 18commonly deployed options. 19 20While WPS can enable more home networks to use encryption in the 21wireless network, it should be noted that the use of the PIN and 22especially PBC mechanisms for authenticating the initial key setup is 23not very secure. As such, use of WPS may not be suitable for 24environments that require secure network access without chance for 25allowing outsiders to gain access during the setup phase. 26 27WPS uses following terms to describe the entities participating in the 28network setup: 29- access point: the WLAN access point 30- Registrar: a device that control a network and can authorize 31 addition of new devices); this may be either in the AP ("internal 32 Registrar") or in an external device, e.g., a laptop, ("external 33 Registrar") 34- Enrollee: a device that is being authorized to use the network 35 36It should also be noted that the AP and a client device may change 37roles (i.e., AP acts as an Enrollee and client device as a Registrar) 38when WPS is used to configure the access point. 39 40 41More information about WPS is available from Wi-Fi Alliance: 42http://www.wi-fi.org/wifi-protected-setup 43 44 45wpa_supplicant implementation 46----------------------------- 47 48wpa_supplicant includes an optional WPS component that can be used as 49an Enrollee to enroll new network credential or as a Registrar to 50configure an AP. The current version of wpa_supplicant does not 51support operation as an external WLAN Management Registrar for adding 52new client devices or configuring the AP over UPnP. 53 54 55wpa_supplicant configuration 56---------------------------- 57 58WPS is an optional component that needs to be enabled in 59wpa_supplicant build configuration (.config). Here is an example 60configuration that includes WPS support and Linux wireless extensions 61-based driver interface: 62 63CONFIG_DRIVER_WEXT=y 64CONFIG_WPS=y 65 66 67WPS needs the Universally Unique IDentifier (UUID; see RFC 4122) for 68the device. This is configured in the runtime configuration for 69wpa_supplicant (if not set, UUID will be generated based on local MAC 70address): 71 72# example UUID for WPS 73uuid=12345678-9abc-def0-1234-56789abcdef0 74 75The network configuration blocks needed for WPS are added 76automatically based on control interface commands, so they do not need 77to be added explicitly in the configuration file. 78 79WPS registration will generate new network blocks for the acquired 80credentials. If these are to be stored for future use (after 81restarting wpa_supplicant), wpa_supplicant will need to be configured 82to allow configuration file updates: 83 84update_config=1 85 86 87 88External operations 89------------------- 90 91WPS requires either a device PIN code (usually, 8-digit number) or a 92pushbutton event (for PBC) to allow a new WPS Enrollee to join the 93network. wpa_supplicant uses the control interface as an input channel 94for these events. 95 96If the client device has a display, a random PIN has to be generated 97for each WPS registration session. wpa_supplicant can do this with a 98control interface request, e.g., by calling wpa_cli: 99 100wpa_cli wps_pin any 101 102This will return the generated 8-digit PIN which will then need to be 103entered at the Registrar to complete WPS registration. At that point, 104the client will be enrolled with credentials needed to connect to the 105AP to access the network. 106 107 108If the client device does not have a display that could show the 109random PIN, a hardcoded PIN that is printed on a label can be 110used. wpa_supplicant is notified this with a control interface 111request, e.g., by calling wpa_cli: 112 113wpa_cli wps_pin any 12345670 114 115This starts the WPS negotiation in the same way as above with the 116generated PIN. 117 118 119If the client design wants to support optional WPS PBC mode, this can 120be enabled by either a physical button in the client device or a 121virtual button in the user interface. The PBC operation requires that 122a button is also pressed at the AP/Registrar at about the same time (2 123minute window). wpa_supplicant is notified of the local button event 124over the control interface, e.g., by calling wpa_cli: 125 126wpa_cli wps_pbc 127 128At this point, the AP/Registrar has two minutes to complete WPS 129negotiation which will generate a new WPA PSK in the same way as the 130PIN method described above. 131 132 133If the client wants to operate in the Registrar role to learn the 134current AP configuration and optionally, to configure an AP, 135wpa_supplicant is notified over the control interface, e.g., with 136wpa_cli: 137 138wpa_cli wps_reg <AP BSSID> <AP PIN> 139(example: wpa_cli wps_reg 02:34:56:78:9a:bc 12345670) 140 141This is used to fetch the current AP settings instead of actually 142changing them. The main difference with the wps_pin command is that 143wps_reg uses the AP PIN (e.g., from a label on the AP) instead of a 144PIN generated at the client. 145 146In order to change the AP configuration, the new configuration 147parameters are given to the wps_reg command: 148 149wpa_cli wps_reg <AP BSSID> <AP PIN> <new SSID> <auth> <encr> <new key> 150examples: 151 wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 testing WPA2PSK CCMP 12345678 152 wpa_cli wps_reg 02:34:56:78:9a:bc 12345670 clear OPEN NONE "" 153 154<auth> must be one of the following: OPEN WPAPSK WPA2PSK 155<encr> must be one of the following: NONE WEP TKIP CCMP 156 157 158Scanning 159-------- 160 161Scan results ('wpa_cli scan_results' or 'wpa_cli bss <idx>') include a 162flags field that is used to indicate whether the BSS support WPS. If 163the AP support WPS, but has not recently activated a Registrar, [WPS] 164flag will be included. If PIN method has been recently selected, 165[WPS-PIN] is shown instead. Similarly, [WPS-PBC] is shown if PBC mode 166is in progress. GUI programs can use these as triggers for suggesting 167a guided WPS configuration to the user. In addition, control interface 168monitor events WPS-AP-AVAILABLE{,-PBC,-PIN} can be used to find out if 169there are WPS enabled APs in scan results without having to go through 170all the details in the GUI. These notification could be used, e.g., to 171suggest possible WPS connection to the user. 172 173 174wpa_gui 175------- 176 177wpa_gui-qt4 directory contains a sample GUI that shows an example of 178how WPS support can be integrated into the GUI. Its main window has a 179WPS tab that guides user through WPS registration with automatic AP 180selection. In addition, it shows how WPS can be started manually by 181selecting an AP from scan results. 182 183 184Credential processing 185--------------------- 186 187By default, wpa_supplicant processes received credentials and updates 188its configuration internally. However, it is possible to 189control these operations from external programs, if desired. 190 191This internal processing can be disabled with wps_cred_processing=1 192option. When this is used, an external program is responsible for 193processing the credential attributes and updating wpa_supplicant 194configuration based on them. 195 196Following control interface messages are sent out for external programs: 197 198WPS-CRED-RECEIVED <hexdump of Credential attribute(s)> 199For example: 200<2>WPS-CRED-RECEIVED 100e006f10260001011045000c6a6b6d2d7770732d74657374100300020020100f000200081027004030653462303435366332363666653064333961643135353461316634626637313234333761636664623766333939653534663166316230323061643434386235102000060266a0ee1727 201